Page 92 - Medical Parasitology_ A Textbook ( PDFDrive )

Intestinal Nematodes: Soil-Transmitted Helminths (STH) 85

Intestinal infection by adult worm is usually asymptomatic. The clinical features,
if present, are due to nutritional and toxic effects. The nutritional effects are usually
seen when there is heavy worm burden. The worms interfere with proper digestion
and absorption of food. Ascariasis may contribute to protein-energy malnutrition
and vitamin A deficiency. The toxic effects are due to hypersensitivity to the worm
antigens and may be manifested as fever, urticarial and angioneurotic oedema.
Ascariasis may cause complications due to mechanical effect. Masses of worms
may cause intestinal obstruction. Ectopic migration is a complication of ascariasis
due to a few factors, e.g. fever and worms seeking mates. The worm may migrate up
or down along the intestine. It may block the biliary or pancreatic ducts causing
acute biliary obstruction or pancreatitis. It may enter the liver parenchyma causing
liver abscesses. The worm may go up the oesophagus and come out through the
mouth or nose. It may obstruct the appendix causing appendicitis. It may lead to
peritonitis when it perforates the intestine at weak spots such as typhoid or tubercu-
lous ulcers or through suture lines.

Diagnosis
1. Microscopic examination
Detection of eggs in faeces.
2. Gross examination
The adult worm can occasionally be detected in stool.

Treatment
Pyrantel pamoate (11 mg/kg (maximum 1 g) orally once), albendazole (400 mg
orally once), mebendazole (100 mg orally twice daily for 3 days or 500 mg orally
once), or ivermectin (150–200 μg/kg orally once) can be used. These drugs are con-
traindicated in pregnancy except for pyrantel pamoate. Complete intestinal obstruc-
tion is a surgical emergency.

Prevention and Control
Same as for T. trichiura

Strongyloides stercoralis

Distribution
It is found mainly in the tropics, but may also occur in the temperate regions.
Another species S. fullerborni is prevalent in African monkeys. It causes infection
in pygmies in Africa and human infection in Papua New Guinea.

Habitat
The female adult worm is found embedded in the mucosa of the small intestine of
human.